Switchgrass is a hardy, warm season perennial bunch grass of the millet family. It was a component of the native prairie in the Great Plains states and Canada and can grow up to 1.8-2.2 m in height. Switchgrass propagates by rhizomes and seeds produced on spikelets. Switchgrass grown from seed has low vigor and is slow to establish, thus production is decreased until the third year growing year. Switchgrass uses the C4 carbon fixation pathway which allows for improved water use efficiency during its growth period, providing an advantage under drought and high temperature conditions. Once established, switchgrass is also tolerant of flooding and grows rapidly, capturing a significant amount of solar energy and turning it into stored energy in the form of cellulose.
As pasture forage, switchgrass is palatable in the vegetative stage and is grazed by certain animals, used as ground cover to control erosion and farmed as forage for livestock.
Switchgrass is also a good energy crop and can be cut and baled with conventional mowers and balers. Once established in a field, it can be harvested as a cash crop, either annually or semiannually, for 10 years or more before replanting is needed. Switchgrass offers important advantages as an energy crop, in part because it can be liquified, gasified, or burned directly. Ethanol production from switchgrass can provide as much as twenty times more net energy output than corn and removes considerably more CO2 from the air. Switchgrass has the potential to produce the biomass required for production of up to 100 gallons (380 liters) of ethanol per metric ton, which gives switchgrass the potential to produce 1000 gallons of ethanol per acre, compared to 665 gallons for the sucrose from sugarcane and 400 gallons for the starch from corn.
Combustion of switchgrass pellets can result in nearly complete combustion with only 3% to 4% of original mass remaining as ash due in part to switchgrass' lower silica and chloride content as compared to cool season grasses. Ash contents can be further reduced by allowing switchgrass to overwinter in the field, thereby reducing the silica and chloride contents further through the process of leaching. There are also advantages from an ash content perspective to producing switchgrass in sandy soils as opposed to clay soils, again based on silica and chloride contents.
Despite the many advantages that switchgrass has as an energy crop, in order for this grass to fulfill its promise, new varieties of switchgrass are needed that will have increased hardiness and yield, reduce the need for nitrogen and other chemical fertilizers, and allow propagation under widely variant growing conditions.
Plants specifically improved for energy usage can be obtained using molecular technologies. Manipulation of crop performance has been accomplished conventionally for centuries through plant breeding. The breeding process is, however, both time-consuming and labor-intensive. Furthermore, appropriate breeding programs must be specially designed for each relevant plant species.
On the other hand, molecular genetics approaches that introduce and express recombinant nucleic acid molecules allow production of plant species tailored to grow more efficiently and produce more product in unique geographic and/or climatic environments. To this end, there is an ongoing need for genetic sequences and materials to advantageously manipulate plant characteristics such as architecture, biomass, development, composition, conversion efficiency, energy output, confinement, nitrogen use, nutrient uptake, phosphate use, photosynthetic capacity, shade avoidance, cold tolerance, drought tolerance, water use efficiency, stress tolerance, vigor, flowering time and yield to maximize the benefits of energy crops and other economically important crops depending on the benefit sought and the particular environment in which the crop must grow. These molecules may be from the plant itself, and simply expressed at a higher or lower level, or the molecules may be from different plant species.